I also got the onsite invite from BU, and while I'm pleased I'm a little disappointed because during my interview they described this as more of an admissions day where you talk to professors to figure out funding, and that we'd actually have an admissions offer at this point. I also won't be able to make it to the day of, so I'll be speaking with a few faculty earlier in the week.
I haven't heard from my remaining schools (Wharton, Harvard, and NYU Wagner), but I did notice that Wharton sent out a batch of interview invitations last week. Considering the average GRE quant score for the PhD programs there is a 797, I didn't have high hopes for being one of the top contenders there...
Best of luck to everyone else, and hopefully I'll see some of you at the Brown recruitment day next week!